Long or hard session: should you eat during exercise?
A half marathon, a three-hour ride, a day-long tournament: beyond an hour, fuelling on the move becomes a real question. Here are the markers from the International Olympic Committee and professional bodies, translated into simple foods.
The essentials
- Under an hour, no: water is enough.
- Beyond an hour of sustained effort, the guide is 30 to 60g of carbohydrate an hour.
- Rehearse your fuelling in training, never for the first time in competition.
How long does a session have to be before I need to refuel?
From about an hour of sustained effort. Below that, your stores and a meal eaten two to three hours earlier are enough, with water. The British Dietetic Association sets the threshold this way: if you exercise hard for longer than an hour, taking in carbohydrate as you go can enhance performance.
The International Olympic Committee adds detail. In competition lasting about an hour, even small amounts of carbohydrate have an effect on physical and mental performance. The longer the event, the more is needed.
A 50-minute dance fitness class does not fall into this bracket. A half marathon, a long bike ride or a handball tournament with several matches in a day does.
How much, and from which foods?
The usual guide is 30 to 60 grams of carbohydrate an hour. It comes from a scientific review led by a researcher at the Australian Institute of Sport. For events lasting more than two and a half to three hours, the target rises to as much as 90 grams an hour according to the International Olympic Committee, a level that concerns marathon runners, triathletes and long-distance cyclists.
UK dietitians give equivalents. About 50 grams of carbohydrate is:
- two medium to large bananas;
- 15 dried apricots;
- 500ml of fruit juice;
- 800ml of isotonic sports drink.
A banana an hour, topped up with a few pieces of dried fruit, puts you near the bottom of the range. These are general guides, to be adjusted with a professional.
What should I drink, and do I need salt?
Drink enough to limit water loss, without overdoing it. The International Olympic Committee gives athletes the rule: replace what sweat takes away, without drinking beyond it. The American College of Sports Medicine adds that sweat rates vary widely from one person to the next and recommends a personalised plan, built with a professional.
Salt becomes useful when you sweat heavily, especially beyond about two hours, according to the Committee. A drink containing carbohydrate and electrolytes then has an advantage over water alone in certain circumstances, the American College notes. In hot conditions, a chilled drink helps too.
How do I avoid stomach trouble on the day?
By rehearsing your fuelling in training. The International Olympic Committee asks this of athletes: practise taking in carbohydrate during sessions to build a personal strategy and limit stomach and gut problems. That is how you find out what you tolerate.
Three practical rules follow:
- nothing new on race day, neither food nor drink;
- the same fuelling on your last two or three long outings;
- a note after each trial on what you took and how it sat with you.
Shop-bought gels and drinks are not compulsory. UK dietitians present them as a possible aid for training that lasts several hours or is very intense. A banana, dried fruit, diluted juice in the bottle: whatever goes down well in training makes a solid base for the day itself.
Your fuelling plan, step by step
Do
- An outing of 90 minutes to two hours: a banana an hour, water, a few pieces of dried fruit.
- A day-long tournament: a banana, bread or fruit juice between matches.
- A fuelling trial on every long outing in the final weeks.
- A chilled drink in the bottle when it is hot.
Avoid
- A food or drink you have never tested, on competition day.
- Drinking so much that you feel bloated.
- Refuelling during a session of less than an hour.
When to seek advice
Before an event lasting more than two hours, an appointment with a sports dietitian lets you build a personal fuelling plan, as professional bodies recommend. See your doctor if you have diabetes, repeated stomach trouble during exercise, faintness or cramps that return despite your adjustments.
General guidance for healthy adults. It does not replace advice from a health professional who knows your situation.